Using the generation of Brunel harmonics by elliptically polarized laser pulses for high-resolution detecting lower-frequency radiation

We propose to use the generation of even Brunel harmonics (BHs) by optical laser pulses for high-resolution gas-biased coherent detection of lower-frequency radiation in terahertz and mid-infrared ranges. BHs arise due to the acceleration of electrons liberated in the tunneling ionization process, and BHs pulses are much shorter than the laser ones. The latter makes it possible to significantly increase the tempo-ral resolution of sampling detection compared to the use of cubic response of bound electrons generating the second harmonic of the gating pulse. However, as we show by solv-ing the time-dependent Schrodinger equation for the helium atom, for an intense linearly polarized laser pulse, the atomic response contains a broadband noise signal that interferes with BHs and allows the detection of very high electric fields only. We show that the nature of this noise is related to the population of the Rydberg states of the atom, which can be effectively suppressed by using elliptical polarization of the gating pulse. (c) 2022 Optica Publishing Group

Automated summary

The study proposes the use of optical laser pulses to generate Brunel harmonics (BHs) for high-resolution gas-biased coherent detection in terahertz and mid-infrared ranges. However, the strong linearly polarized laser pulse introduces broadband noise interference, which can be effectively suppressed by using elliptical polarization of the gating pulse.